1. Field of the Invention
This invention generally relates to spas and hot tubs and more specifically to control systems and circuits utilized in such spas and hot tubs.
2. Description of the Related Art
Pools, whirlpool spas, hot tubs and related systems typically include a tub for holding water, a pump for circulating the water and a heater. The pump draws water from the tub through a drain, forces the water through the heater and out through jets into the tub, thereby circulating the water and causing it to be heated by passing it through the heater.
When the pump is operating, personal contact with the drain can be dangerous, painful or even fatal. When the body or hair of a person is positioned in close proximity to the drain, the body or hair may completely or partially block the drain, thereby creating a vacuum or entrapment. This can cause entrapment of the person. Many pumps used in such systems, if obstructed, can draw a partial vacuum at the drain that may exert sufficient suction force to prevent a person from pulling free of the drain. Even if the person can pull free of the drain, bruises, welts, or other damage may result.
One approach to overcoming this safety hazard has been the use of multiple drains or suction ports and suction covers or grates which are formed to minimize the possibility of hair entanglement and prevent an airtight seal between a person""s body and the drain. However, there are many systems still in use that were installed prior to the recognition of this safety hazard. It can be extremely difficult and expensive to rebuild or retrofit such existing systems to conform to modern safety regulations. Mechanical systems such as vacuum breakers and a Stengil switch can be retrofitted into such systems to give some measure of protection. However, such systems are not particularly sensitive to partial conditions of entrapment such as hair entanglement.
In addition, it is the current trend in safety regulations to require that such systems have a flow sensor. One use of flow sensors is to insure that water is flowing through the system and the heater before the heater is activated. Such flow sensors have typically been implemented as an electro-mechanical flow switch consisting of a microswitch activated by a diaphragm in contact with the water. These pressure switches are usually set to an arbitrarily low value, which may be 10 to 20 percent of the actual full pressure of the system in normal operation. Exceeding this low value is used as an indication that the pump is working. However, it is insufficient to detect significant pressure changes such as would be caused by partial entrapment.
In addition, it is required to supply electrical power to the pressure sensor and accompanying circuitry. To minimize the possible risk of electrocution, it is desirable to limit the amount of current at locations that could come in contact with water in the spa through a fault or failure.
The present invention provides a safety circuit which can send a signal to a control circuit to automatically remove electrical power from a device such as a pump in response to an indication of a change in the pressure in the circulating system.
The safety circuit can contain a sensor that generates a signal representative of the pressure generated by the pump. A microcontroller is coupled to receive the signal from the sensor and is configured to store a first level indicative of a signal received from the sensor at a first time. The microcontroller is configured to compare the first level with a second level indicative of a signal received from the sensor at a second time. The microcontroller is configured to generate a control signal when the comparison between the two levels indicates a change in pressure which exceeds a predetermined amount of change. The microcontroller sends the control signal to the spa control circuit. The spa control circuit controls the application of electrical current to the pump. An electrically controlled switch is coupled to receive a signal from the spa control circuit and is configured to control application of electrical power to a device, such as a pump, in response to that signal.
In one aspect of the invention the sensor is a pressure sensor which is capable of producing a signal representative of changes in pressure in the spa system. The safety circuit can be used to detect conditions of entrapment or partial entrapment and immediately shut off the pump in the spa when such conditions are detected.
In another aspect of the invention, the safety circuit contains a constant current source to limit the electrical current available at locations that could come in contact with water.
These and other features and advantages of the invention will be readily apparent to those skilled in the art from the following detailed description of embodiments of the invention with reference to the accompanying drawings.